1. Field of the Invention
This invention relates generally to substrate fabrication, and more particularly to semiconductor wafer preparation equipment.
2. Description of the Related Art
As is well known, semiconductor devices are fabricated from semiconductor wafers, which are subjected to numerous processing operations. These operations include, for example, impurity implants, gate oxide generation, inter-metal oxide depositions, metallization depositions, photolithography pattering, etching operations, chemical mechanical polishing (CMP), etc. Although these processes are performed in ultra-clean environments, the very nature of many of the process operations is to blame for the generation of surface particles and residues. For instance, when CMP operations are performed, a film of particles and/or metal contaminants are commonly left behind.
Because surface particles can detrimentally impact the performance of an integrated circuit device, wafer cleaning operations have become a standard procedural requirement after certain process steps. Although cleaning operations are rather procedural, the equipment and chemicals implemented to perform the actual cleaning are highly specialized. This specialization is important because each wafer, being at different stages of fabrication, represents a significant investment in terms of raw materials, equipment fabrication time, and associated research and development.
To perform the cleaning operations in an automated manner, fabrication labs employ cleaning systems. The cleaning systems typically include one or more brush stations in which wafers are scrubbed. Each brush station includes a pair of brushes, such that each brush scrubs a respective side of a wafer. To enhance the cleaning ability of such brush stations, it is common practice to deliver cleaning fluids through the brush (TTB). TTB fluid delivery is accomplished by implementing brush cores that have a plurality of holes that allow fluids being fed into the center of the brush core at a particular pressure to be released into an outer brush surface. The outer brush surface is made out of a very porous and soft material so that direct contact with the delicate surface of a wafer does not cause scratches or other damage. Typically, the outer brush surface is a made out of polyvinyl alcohol (PVA) foam. Although, other materials such as nylon, mohair or a mandrel wrapped with a polishing pad material can be used.
As semiconductor design and performance requirements continue to increase, cleaning engineers are also challenged to improve their associated processes. To meet these demands, the same cleaning equipment is now being used to perform operations other than basic de-ionized (DI) water cleaning. Such operations include the application of sophisticated chemicals TTB to remove particulates and/or to etch precision amounts of materials from the surfaces of a wafer. Although much research and development goes into the design of cleaning and etching chemicals, the effectiveness of such chemicals is only as good as their delivery and application onto the surface of a wafer.
In a conventional wafer preparation system, in which wafer scrubbing is performed, the system typically connects an end of each brush to its own drive train and external motor to enable rotation of the brush over a wafer. FIG. 1 illustrates a prior art implementation 10 in which a single brush 12 is mounted on a brush core 14. The brush core 14 has a first end 14a that is connected to a drive train 16 and a second end that is connected to a wall 11b. The drive train 16 typically has a number of gears 16a that enable a motor 18 to rotationally drive the brush 12 at a desired rate. The drive train 16 is typically contained inside a wall 11a and proximate to the first end of the brush core 14a. The motor 18 is thus coupled to the drive train through the wall 11a. The brush core 14 is a core that can allow fluids to be input through a fluid input 13.
A problem with this conventional implementation is that the brush core 14 is required to move in relation to the walls 11a and 11b while maintaining the drive train 16 and the motor 18 connections so they can function. Because the brush core 14 needs to pivot with respect to the walls 11a and 11b, the brush core 14 experiences some unstable movement during operation. For example, slider couplers 15 and 17 are designed with a level of tolerance to enable the brush core 14 to be decouple and allow the brush 12 to be changed or serviced. This tolerance therefore causes the unstable movement that is known to cause an improper application of chemicals TTB or application of pressure onto the wafer being cleaned, etched, or buffed. The unstable movement is also referred to uncontrollable brush skewing. However, the goal of this conventional design is to maintain the brush core 14 stable with respect to the drive train 16 and the walls. It is also a goal to prevent a skewed brush from contacting an entering water, or have a brush that contacts the wafer at a skewed orientation because the wafer itself is entering skewed. Although attempts are constantly being made to improve the stability of the brush core 14 during operation, the brush core 14 nonetheless needs to have a degree of free movement (e.g., non-controllable brush skewing) to enable the slide couplers 15 and 17 of the drive train 16 to work properly.
Because traditional cleaning typically only included the application of DI water and/or ammonia based chemicals, the uneven application of a brush and thus the fluids through the brush core did not in many cases detrimentally impact cleaning performance. However, because most cleaning systems are now required to also apply engineered chemicals, such as hydrofluoric acid (HF) containing etch chemicals, any uneven application of the brush and chemicals will have a sever impact on the wafer being processed. For instance, if more HF is applied to one part of the wafer and less is applied to another part of the wafer, the surface of the processed wafer may exhibit performance impacting etch variations due to experienced chemical concentration variations.
In view of the foregoing, there is a need for improved brush designs that enable the controlled and programmable application of the brush onto the surface of a wafer during wafer preparation.
Broadly speaking, the present invention fills these needs by providing a brush core having an internal motor. Removing the external drive train allows each end of the brush core to be independently position calibrated to achieve the desired contact or pressure with a substrate during substrate preparation. The substrate can be any substrate that may need to undergo a scrubbing operation to complete a cleaning operation, etching operation, buffing operation or other preparation. For instance, the substrate can be a semiconductor wafer, a hard drive disk, or any other type of workpiece needing preparation. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a brush core for use in substrate preparation is disclosed. The brush core includes a cylindrical inner motor case that has a first diameter. A cylindrical brush core shell having a second diameter that is greater than the first diameter is also provided. A separation between the first diameter and the second diameter defines a fluid distribution channel of the brush core. A motor is encapsulated within the cylindrical inner motor case. Motor end caps are configured to seal the motor within the cylindrical inner motor case, and a bore is defined in each of the motor end caps. A shaft is positioned through the motor, penetrating both end caps, and a first end of the shaft has a fluid inlet for providing a fluid to the fluid distribution channel. The shaft also has a second end that is directly opposite the first end of the shaft. Because the motor and associated drive train are contained within the brush core, both the first end and the end of the shaft can be positioned independently to achieve the desired brush core skew. In this embodiment, if desired, the shaft can be controlled to achieve a desired pressure contact zone over the substrate being prepared. The positioning is capable of being performed by way of position controllers that can be computer programmed, manually adjusted, or automatically adjusted depending upon a detected skew condition of a substrate. In this manner, if desired, the brush can make equal contact with the surface of the substrate along the entire length of the brush.
In another embodiment, a brush core is disclosed. The brush core is connected between a first end and a second end of a non-rotating shaft. A motor is contained within the brush core for rotating the brush core around the non-rotating shaft. The first end and the second end are each capable of being adjusted to calibrate and position the brush core. The calibrated position of the brush core can be set to compensate for a skewed substrate, or to achieve a desired pressure application profile over the substrate.
In yet a further embodiment, a method of making a brush core for use in substrate preparation is disclosed. The method includes: (a) providing a motor; (b) forming an internal motor case for containing the motor; (c) forming a brush core shell around the internal motor case, the brush core shell is separated from the internal motor case, the separation defines a fluid distribution channel, and the brush core shell has a plurality of holes that define paths out of the fluid distribution channel; (d) forming motor end caps for closing a first end and a second end of the brush core shell and the internal motor case; and (e) providing a shaft that is configured to be inserted into a bore of the motor end caps, and the shaft has a fluid inlet for providing a fluid flow to the fluid distribution channel and out of the plurality of holes. At the other end of the shaft, electrical connections can be fed to the motor.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.